The Fall of the House of Tank Drive

Copying from this post: Swerve Drive at the 2022 Championship

121/192 - 63% of the robots in the playoffs used swerve
102/144 - 71% of the Captains/1st/2nd robots in the playoffs used swerve
22/24 - 92% robots on Einstein used swerve

Tank drive is still and will continue to be viable, but swerve has taken hold at a rate that outpaced even the biggest expectations. Not saying this is a bad thing, but it’s definitely a thing.


I think that the biggest reason we saw swerve being so dominant this year was the pathing for scoring. Look at 2020 you dont need to have a swerve to be competitive that year since for the most part its a straight line to the scoring zone, 2016 same thing, 2018 same thing. The problem (if you want to call it that) was that teams that could drive sideways could more easily line up and shoot at the goal. As long as next year has a less rounded path to scoring I don’t see swerve being nearly as nessessary as it was this year.


I’m not entirely sold that swerve, if maintained properly, can’t last for 2-3 seasons and bring the overall cost down. We played in 88 official matches this year and probably another 100+ very aggressive matches on our practice field and they’ve held up just fine. The MK4’s are pretty bullet proof if you keep them greased. Now, we did have to replace a bearing and all our belts had to be changed before DCMP but those are inexpensive.


There is no practical downside or tradeoff to using swerve on a flat field, aside from out of pocket cost.

There are tons of power distribution slots, especially 40A slots.

There are unlimited motors and no need for shifting anymore.

Brushless motors with integrated encoders simplify the wiring and part count.

COTS swerve modules are extremely well designed and easy to integrate. You can put together a swerve chassis in an hour.

Off-the-shelf software exists and is only going to get better.


Sure. That’s one of the reasons why I don’t think brushless motors aren’t in and of themselves a major hurdle–you can reuse them for quite a while, amortizing the cost over several years. A solid swerve drive can be maintained until it’s no longer competition caliber, then used as a training platform for drivers and programmers.

But as a hurdle, swerve has issues above and beyond cost. From hardware to software to maintenance, even easy swerve is significantly harder than anything tank.

And maybe this is all fine in the end, and by 2024 we’ll all be Thriftybotting and MK4ing around carpet to the extent that even rookie teams are assembling COTS kits, tossing on some plug-and-play software, and enjoying the benefits of swerve. Maybe.


I think the biggest loss from the rise of swerve will be the discussions that are had on day 1 of build season where someone says “What drivetrain should we run this year?” The conversation that followed used to have nuance and healthy argument with valid points.

“Are we willing to give up 8 PDP slots?” … not a question anymore
“Do we have the machining skills to do it?” … not a question anymore
“Can our programming team write robust code for it?” … not a question anymore.

The only real reason not to do swerve…
“Can we afford it?”

I think that’s the shame. The only barrier left for swerve is cost. That’s how you raise the ceiling and leave the floor right where it is. The rich get richer.

I would fully support the FRC manual next year having a rule along the lines of “Only 16 PDH slots may be used to power motors.” That way swerve teams have to make an engineering choice, and they must give something to get something. I think a rule like this should be in effect until there is a KOP Swerve drivetrain. Just my opinion.


We’re going to find that one out during this off-season…


There is so much public code out there, made available by great teams and the COTS swerve suppliers. It’s a worthwhile experience to write your own code, but it’s less of a question of “can we do it?”

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We have a Thrifty Swerve built and wired, so next step, clearly, is to see what we can make of it.

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I feel like just using really high gear swerve like our team this year could work on fields with a lot of bumps or traction-related obstacles. To bring more drive train diversity back, there needs to be an intentional decision to make a purposeful “anti-swerve” field layout. I don’t know what it would look like, but you can’t just throw a bump on the field and call it a day.


FRC has always had some form of a more subtle arms race - be it manufacturing sponsor, fancy 3D printer, in-house tooling, time spent in the shop, and/or space for a practice field. Only recently have we been able to point a finger at a widely-quantifiable target like COTS mechanisms as part of it.

The subtle reality of the race was why the BOM was a terrible metric of true robot cost for any given season. IMO, it is also why we should focus less on fairness and more on inclusion. Different parts of the country/world have, unfairly or not, better access to one or more of the resources listed above. Yet at least COTS and no-bag gives every team the opportunity to leverage more of the universally-available resources available to teams if they put it what’s necessary to acquire them: time and money. I can’t leverage the expertise from a CNC sponsor that doesn’t exist in my area. However, I can recruit more students/mentors, use them to help fundraise, and purchase a swerve module.

The GDC can balance out the dominance of swerve without going so crazy that they make a game the KOP can barely play.

  • '18, ‘19’, and '20 (with the steel berm) were great examples of games where swerve drive was an advantage, but it wasn’t SO much of an advantage that we didn’t see any KOP drivetrains on Einstein.
  • Open field games like '13, '14, and '17 would have been dominated by swerve had the COTS modules been available with BLDC’s.

Crazy how quickly the paradigm has shifted: Why do high-tier teams not use Swerve Drive

But I think this is it right here:

^This paradigm has shifted. Swerve is less parts, less motors, less development, less code, less resources, and less compromises than it used to be. It’s still more of most of those things than the Kit of Parts chassis, but it’s much less daunting. I’d also argue swerve is easier to drive when the field centric code is good.

I think it’s likely we see next year’s game have some obstacles that make off-the-shelf swerve harder to run, but only time will tell.


I hope not. In general, I think FRC is most exciting when teams are able to zip around the field. Terrain obstacles tend to disproportionately affect lower resource teams, so I think any obstacles put on the field to deter swerve drives would just end up hurting the teams these rules are in theory are trying to protect.


This is going to be less of an issue over time. The initial investments companies have made in design will pay off, and eventually (soon, maybe) someone will challenge the pricing structure. It’s also quite possible that teams with moderate machining capabilities will just copy the CAD and make the parts themselves verbatim. A $365 module this year is next year’s $300 module, and 2024’s $100 module.


And moving sideways has been conclusively demonstrated NOT to be a waste of time, after all.

But about that flat field …


The solution I propose is making a shorter field path involving obstacles which will benefit tank drive which would be able to drive over, and a longer path for swerve or a more defendable path perhaps. Then teams have to really think which drivetrain choice provides the most benefit for how they would like to play the game.

Yes, unless the KOP comes with swerve it places teams at a massive disadvantage that use the KOP. Which means that most rookie or fledgling teams will nbe dominated by swerve drives, which generally means more established teams with sufficient sponsorship. Which leads to discouraged teams using non-swerve, even if their robot is amazing in all other aspects of gameplay. Which is likely to result in more rookie team failures.


An interesting thought exercise is to think about what robots and gameplay would have looked like in prior games if we had the same robot rules + COTS components and software that we have today.

Can you imagine Aerial Assist or Ultimate Ascent (for example) with 6 brushless swerves on the field?


:heart_eyes: :heart_eyes: :heart_eyes: :heart_eyes: :heart_eyes: :heart_eyes:


Aerial assist with today’s tech would be incredible. I would pay good money to see it happen


All someone has to do* is replace the 4 turning motors with something more cost effective, and the price point won’t be too far from a custom skid steer.

*Yea, right…

Maybe this involves differential swerve with a servo to control the phase. There’s a mechanical device that can control the phase between two rotating coaxial shafts, using a differential. It was so long ago that I can’t remember what it was called, but it was used to control the pitch of quadcopter blades while using a single central power plant for blade rotation speed.

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